Power lead arrangement for electric arc furnace



Nov. 24, 1970 I H. SCHEMG 3,542,932

POWER LEAD ARRANGEMENT FOR ELECTRIC ARC FURNACE Filed June 3, 1969 1 2Sheets-Sheet 1 I 15 r 1a 19 //////A L I I L I L L 1 I3 I L L N I C) Nov.24, 1970 H. SCHEIDIG POWER LEAD ARRANGEMENT FOR ELECTRIC ARC FURNACE IFiled June 5, 1969 2 Sheets-Sheet 2 FIG. 3

United States Patent US. Cl. 13-34 8 Claims ABSTRACT OF THE DISCLOSUREPower lead arrangement for a vacuum electric furnace with a consumablefurnace electrode wherein the power lead is resiliently mounted on thefurnace and attached by clamping to the top of the crucible such thatthe power lead will be properly in contact with the crucible even thoughthe furnace and the crucible may be misaligned.

The invention relates to a power lead arrangement for an electric arcfurnace with consumable furnace electrodes wherein the furnace body isvertically movable in a suspension mechanism and adapted to be set downon a crucible.

Known electric arc furnaces for making metals by melting in a vacuumhave furnace bodies mounted in a suspension mechanism which are loweredon the previously charged crucibles. After melting of the cruciblecontents, the crucible with its charge is carried off for furtherprocessing, and the furnace body is connected with a new crucible. Aconsumable electrode is located within the furnace body and produces theelectric arc with the charge. It is particularly difficult to provide aconductive current path to the bath and to the furnace electrode becausea substantial influence of the transfer resistance at the contact pointsmust be expected on account of the high current values at relatively lowpotential differences. In known vacuum arc furnaces of the kinddescribed the power leads are arranged in such a manner that thepositive current supply to the crucible is provided by fixedly installedbus bars which are led to the crucible or crucibles from one side andhorizontally, are divided symmetrically ahead of the cruciblecircumference, and are then connected to two diametrically oppositecontact points at the crucible. The furnace electrode is connected withthe negative terminal by means of watercooled flexible cables. Thecurrent conducting bars which approach the crucible from the side have astrong magnetic field which, in the event of asymmetry, has anunfavorable effect on the metal melt in the crucible and on the shape ofthe electric arc. The metal melt in the crucible may be caused torotate, and the arc to be blown off laterally. A non-homogeneous melt iscaused thereby in which certain ingredients of the melt are accumulatedin certain areas, and there cause undesirable segregation or occlusion.

With the above in view it is an object of the invention to provide apower lead arrangement for an electric arc furnace with consumablefurnace electrode which insures good contact of the current supplyconductor with the crucible with uniform distribution of the currentflow over the crucible circumference. In order to achieve this object,it is being proposed, according to the invention,

to provide contact elements at least at two diametrically oppositelocations which elements are insulated from the furnace body and adaptedto be connected with the electric current supply, the contact elementsbeing arranged relatively movable to the crucible surface in such amanner that they engage circumferential portions of the crucible underpressure for the purpose of providing contact after the furnace body wasset down on the crucible. By an arrangement including contact bodiesinsulated and separate from the furnace body which engagecircumferential portions of the crucible, more specifically on thesurface of the crucible flanges, an adequate contact area with lowcontact resistance is provided even if the furnace axis deviates fromthe crucible axis. At that, it may be advisable to arrange the contactelements on the circumference of the furnace body in symmetricaldistribution relative to the furnace electrode. According to a furtherfeature of the invention, a power lead supplying current to the contactelements or to their supporting mountings may be provided horizontallyin the region of the upper edge of the furnace body with verticallydescending connecting lines for avoiding undesirable mag netic fields inthe area of the electric arc and of the melt. Because the contactelements are located parallel to the axis of symmetry of the cylindricalcrucible, the axial symmetry of the entire arrangement results in auniformly developed magnetic field which cannot exert motive power onthe electric arc and the melt.

A preferred embodiment may be arranged in such a manner that the contactelements are mounted on bus bars which are elastically displaceable onthe furnace body. The elastic mounting may be provided in various waysby means of tension springs or by the elastic properties of the materialor by the supports of the bus bars. It may be advisable to provideadditional clamping elements for connecting the current carrying barswith the crucible, the clamping elements being pivotally mounted on thebus bars, on the crucible, or on the cooling tank according to choice.Such clamping elements capable of being applied under pressure may bearranged advantageously for example on the cooling tank, and may engagesuitably adapted lugs on the bus bars. However, such clamping elementsare required on each cooling tank. According to an advantageousembodiment, clamping elements may also be provided at the lower ends ofthe current carrying bars whereby the total number of required clampingelements is reduced. After lowering of the furnace body on the crucible,the contact elements already engage circumferential portions of thecrucible. When the clamping elements are applied under pressure, theengagement is additionally improved for lowering the contact resistance.The clamping elements may be clamped on manually, but also in a wellknown manner in the are by means of pneumatic or hydraulic devices. Afurther advantage may be achieved by employing the clamping elements asfasteners for fastening the crucible to the cooling tank which envelopsthe crucible.

It may be useful in certain cases to let the furnace body rest on thecrucible in the lowered condition partly without balancing its weight sothat the weight of the furnace body increases the contact pressure ofthe contact elements. Moreover, the pressing force generated by thevacuum may be utilized for enhancing the contact pressure.

The proposed power lead system permits good contacts to be establishedand provides precisely defined current paths symmetrically locatedrelative to the electrode and the melt so that any effect on theelectric arc is properly balanced.

A preferred embodiment of the invention is illustrated in theaccompanying drawing, in which:

FIG. 1 is a perspective view of the essential parts of a furnace;

FIG. 2 is a perspective view of a detail of a part of the furnace; and

FIG. 3 is a section of FIG. 1 taken along the axis thereof.

Referring now to the drawings wherein like numerals refer to like partsthroughout, FIG. 1 shows the essential parts of a furnace. The furnaceconsists of a vacuum tight, cylindrical furnace chamber or body,preferably made of sheet metal. Said furnace body 1 can be raised andlowered by means of a suspension mechanism, not shown, in the drawing.Of this mechanism only tie rods 10 are shown. At the outer circumferenceof furnace body 1, current carrying bars 3 are resiliently mounted onsupports 2 arranged in symmetrical distribution. The lower ends of thebars 3 constitute contact elements 4 which rest on the surface of acrucible flange 5 of the crucible 6. As is evident from the position ofthe bars 3 shown in dotted lines, the resilient mounting is such thatthe bars 3 are always parallel to the axis of symmetry of the crucible 6regardless of the alignment of the furnace body 1 and the crucible 6. Inorder to improve the contact resistance, suitable clamps 7 are providedon crucible 6, and their projections '8 engage corresponding recesses 9of the current conducting bars 3 and increase the contact pressure inthe tensioned condition. Although, as is indicated in the drawing, theaxis of symmetry CD of the crucible is tilted relative to the axis ofsymmetry of the furnace body AB, a reliable contact is provided at thecontact elements. The paths of current flow from the contact points onthe crucible to the melt are also symmetrically distributed so thatdisturbing field effects are eliminated.

From the foregoing it will be noted that tie rods 10 are fastened toroof 11 which permits the movement of a consumable electrode 13 which issurrounded by the furnace chamber 1 as shown in FIG. 3. Shell 14represents a vacuum seal, as in form of several pressure stages,permitting a longitudinal movement of feed rod 12.

Attached to the periphery of the furnace chamber are symmetricallyarranged conductors 3 as indicated. Said conductors are preferably ofcopper and are mounted for example on rubber-metal connections. Theessential characteristics of these supports are that they are goodelectrical insulators. Said conductors 3 are resting with their lowerends which serve as contacts 4 on the upper surface of flange 5 ofcrucible 6. In order to improve the contact between conductors 3 andflanges 5, clamping devices 7 are provided for each conductor. Saiddevices 7 are formed like hooks and their ends 8 extend into openings 9of conductors 3.

It will be further noted that each clamping device 7 consists of a hook15 and a lever 16, the latter being movably attached to an outer casing17 of crucible 6 by means of bolt 18. Said bolt is preferablyresiliently mounted in order to adjust differences in the geometry ofthe contact pieces or'members. Hook 15 and lever 16 are interconnectedby means of bolt 19. The coordination of book 15, lever 16 and bolts 18and 19 is such that by a downward movement of lever 16 by handle 20,hook 15 presses conductor 3 against flange 5 in which position theclamping device is self-arrested after having passed a dead center.Handle 21 serves to place the clamping device into position whenloosened.

Conductors 3 are, in their first section, led into a position parallelto the axis of the furnace chamber 1 so that any disturbance of the melt22 (FIG. 3) in crucible 6 by an electromagnetic field caused by highcurrent in the conductors 3 is thereby avoided. Furthermore, conductors3 are then bent in a right angle such, that both conductors are still inparallel. At a certain length, both conductors are bent in a circle inopposite direction until they join at cable connection 23, which iselectrically connected to cable 24. The other phase 'is connected to afeed rod 12 by a similar cable 25 and a conductor 26, asdiagrammatically shown.

As shown in FIG. 3, a section is given through the arc furnace along theaxis of furnace chamber 1 and crucible 6 wherein the consumableelectrode 13 suspended and moved by feed rod 12 and is coaxial with theaxis. An arc is drawn between the lowest end of electrode 13 and melt22. The heat of the arc, melts the electrode which drips into thewater-cooled copper crucible 6 thereby forming an ingot by graduallyfreezing from the bottom (not shown) of the crucible. The outer casing17 of the crucible forms a so-called cooling jacket (Kuhltopf), as thespace between crucible and casing is filled with water. The intermediatecylindrical wall 27 serves as guiding means for the circulating coolingwater. It is to be noted that clamping device 7 presses flange 28 of theouter casing 17 against flange 5 of crucible 6, the tightness beingachieved by intermediate annular gasket 29.

The embodiment of the invention functions as follows:

The axis of crucible 6 and outer casing 17 may be tilted against theaxis A-B of furnace chamber 1 in normal position, as shown by the dottedline C-D in FIG. 3.

If after charging furnace chamber 1 with a new electrode 13, theassembly is lowered by tie rods 10 of the suspension arrangement,furnace chamber 1 by itsflange 31 would touch gasket 30 on crucibleflange 5 in the first instant only in one single point. It should benoted that the deviation of the axis is very small and the position ofthe dotted lines A-B and C-D- is somewhat exaggerated. Thus, due to theweight of the furnace chamber vacuum tightness is achieved, since gasket30 is, to a certain degree, elastic. In the prior art, however, thecontact elements are not elastic.

In such a case a contact between furnace chamber and crucible wouldnormally be poor and unsymmetrical. By means of the elastic supports 2,however, conductors 3 can follow the tilted position of the crucible andreach the position as indicated by the dotted lines. Hence, the contactpressure remains equal on both sides of crucible flange 5 and thecontact surfaces of conductor 3 and flange 5 are in parallel which ishighly important for good conductivity to obtain a clean melt.

It will be noted that the herein disclosed arrangement is applicable tovacuum electric arc furnaces or to nonvacuum electric arc furnaces.

I claim:

1. Power lead arrangement for an electric arc furnace with a consumablefurnace electrode in which a furnace body vertically movable in asuspension mechanism is adapted to be lowered onto a crucible,characterized in that contact elements are provided on said furnace bodyat least in two diametrically opposite locations, said cHitact elementsbeing insulated from said furnace body and capable of being connectedwith an electrical current supply, said contact elements being furtherarranged relatively to the supporting surface of the crucible wherebythey engage circumferential portions of the crucible under pressure forproviding contact after lowering of the furnace body on said crucible.

2. The arrangement according to claim 1 characterized in that saidcontact elements are arranged on the circumference of said furnace bodyin symmetrical distribution relative to the furnace electrode.

3. An arrangement according to claim 1, characterized inlthat saidcontact elements has leads provided horizontally near the upper edge ofsaid furnace body with vertically descending connecting lines.

4. The arrangement according to claim 1 characterized in that saidcontact elements are provided on current carrying bars mounted on thefurnace body for elastic displacement.

5. The arrangement according to claim 4 characterized in thattensionable clamping elements are provided for connecting the currentcarrying bars and the crucible.

6. The arrangement according to claim 5 character- 5 ized in that thecurrent carrying bars are provided with clamping elements near saidcontact elements.

7. The arrangement according to claim 6 characterized in that saidclamping elements are utilized for fastening said crucible to a coolingtank.

8. The arrangement according to claim 1 characterized in that thefurnace body is suspended in such a manner relative to the crucible thatat least a portion of the weight thereof is available after lowering ofthe furnace 15 body for providing contact pressure to the contactelements.

References Cited UNITED STATES PATENTS 2,227,176 12/1940 Berghaus et al.1331 X 2,551,341 5/1951 Scheer et al. 13-31 3,078,529 2/1963 Cooper etal 1331 X BERNARD A. GILHEANY, Primary Examiner R. N. ENVALL, JR.,Assistant Examiner US. Cl. X.R. 164252; 339147

